Effects of sympathectomy on the cerebral circulation of hypertensive patients

Optimal reverse Trendelenburg position in patients undergoing craniotomy for cerebral tumors

Object

To the authors’ knowledge, repeated measurements of intracranial pressure (ICP), cerebral perfusion pressure (CPP), and the degree of dural tension during different positions on the operating table (reverse Trendelenburg position [rTp]) have not been studied in patients undergoing craniotomy.

Methods

In the present study 53 patients with supratentorial cerebral tumors who underwent craniotomy in the supine position were included. Subdural ICP, mean arterial blood pressure (MABP), CPP, and jugular bulb (JB) pressure were recorded, and the degree of dural tension was analyzed while patients were in the neutral operating position and at 5, 10, and 15° rTp. The optimal operating position was defined as the one at which subdural ICP was as low as possible, and CPP was greater than or equal to 60 mm Hg or as high as possible.

Subdural ICP, MABP, and JB pressure decreased significantly after each 5° change in rTp compared with the preceding position. Dural tension decreased significantly up to 10° rTp, but was unchanged at 15° rTp. At 5° rTp CPP remained unchanged, but it decreased significantly during 10 and 15° rTp. The optimal position in the majority of patients was determined to be 15° rTp.

Conclusions

Before opening the dura mater for craniotomy, repeated measurements of ICP and CPP, in the neutral position and at 5, 10, and 15° rTp, provide valuable information regarding the optimal level of ICP and CPP.

Factors influencing cerebral blood flow and metabolism; a review

The results of studies utilizing the nitrous oxide technic for measuring cerebral blood flow have been reviewed and divided into three groups: (1) those in which cerebral blood flow and metabolism were normal, (2) those in which cerebral blood flow was increased, and (3) those in which cerebral blood flow and metabolism were decreased. The factors which apparently regulate and control cerebral blood flow and metabolism are reviewed and discussed.

Cerebral autoregulation in unconscious patients with brain injury

In 18 unconscious patients with traumatic brain injury, the cerebral autoregulation was tested during the first 2-3 weeks after the acute trauma. Regional cerebral blood flow (rCBF) was measured by the intra-arterial 133xenon washout method before and after an increase of about 20% in the mean arterial blood pressure (MABP) by angiotensin. The difference between MABP and intraventricular pressure (IVP) was used as cerebral perfusion pressure (PP). Simultaneously, ventricular fluid pH, lactate and pyruvate were measured. Regional loss of autoregulation indicated by a 20% flow increase was observed in 29 out of 35 studies (83%), while hemispheric loss of autoregulation was observed in only one study. The results of the autoregulation tests were unrelated to the clinical outcome, the presence of brain-stem lesion, and the ventricular fluid pH, lactate and lactate/pyruvate ratio. In repeated studies, a gradual normalization of the autoregulation was observed about 5 days after the acute trauma.